French Gauge

Despite the obvious benefits of using the metric system and SI units, the medical community persists with various types of bizarre systems of measurement.

One such system is the French catheter scale. To make matters even more confusing, it can be abbreviated in 5 ways:

  • FR or Fr
  • FG (meaning French Gauge)
  • CH or Ch (meaning Charriére)

Joseph Charriére (1803-1876) was the inventor of the French catheter scale. He was a manufacturer of surgical instruments. He worked at a time when there was no standardised system of measurement – different industries and different countries could all do their own thing!

The basic principle of the French catheter scale is that the diameter of the catheter (in mm) is one-third the French size.

So a 10 FR catheter has a diameter of 3.33 mm. Note that this is the outer diameter – so catheters of the same FR size could have different lumen diameters depending on their wall thickness.

Here are 3 common anaesthetic examples:

(1) Y suction catheter

Y suction catheter

The manufacturers of this particular Y suction catheter have just labelled it as “14” without telling you that this is the FR size. The outer diameter is not stated on the packet, but we can work it out to be (14 / 3) = 4.6 mm.

(2) Intubating Bougie

bougie

For this particular bougie, the manufacturer helpfully tells you it’s 14 Fr, and the OD is 4.6 mm (we already worked this out in Example 1). The smallest ETT this bougie will go down is a 5.0 mm. (NB the sizes of ETT’s refer to their internal diameters).

(3) Double Lumen ETT

DLT

This manufacturer states the size as 37 Fr/Ch …. I wonder how many clinicians know that Fr and Ch are actually the same thing? They also state it is a 12.3 mm tube – but unfortunately, they don’t specify that this is the outer diameter (OD)*. Double lumen tubes change shape along their length, so 12.3 mm only applies to the OD at the widest point. The internal diameter of the tracheal and bronchial lumens are each different, and also change shape along the length of the tube!!

* the size in mm stated on a DLT refers to its outer diameter, but for all other ETT’s the size in mm refers to its inner diameter.

I’m sure you can think of other examples… how about urinary catheters, nasogastric tubes, intercostal catheters, and surgical drains!!

It would probably be impossible to change from this system, because it has become so ingrained. Even though few people know the true size of many of these tubes, they seem to know which one to use!

BT_PO 1.99 Lithium

The Hubble Space Telescope’s image of the star V838 Monocerotis 

On the way to work today I listened to a fascinating podcast about an Australian psychiatrist, John Cade, who discovered the benefit of using Lithium in the treatment of bipolar mood disorder. Apparently Lithium was one of the three elements created in the Big Bang along with H and He

Lithium is not a drug we encounter commonly in our anaesthetic practice, although it is still the gold standard treatment for severe bipolar mood disorder and has some interesting toxic effects. As such, I thought it was worthy of a post. None of this is particularly examinable, but still good to know.

Lithium is covered well in Katzung Basic and Clinical Pharmacology (Ch 29)

BT_PO 1.99 Outline the pharmacology of anti-depressant, anti- psychotic, anti-convulsant, anti-parkinsonian and anti- migraine medication

Lithium can mimic the actions of sodium in the generation of membrane potentials T/F

Lithium produces a nephrogenic diabetes insipidus which does not respond to vasopressin T/F

Patients on lithium often exhibit T wave flattening on their ECG T/F

Lithium is completely renally cleared T/F

Leukocytosis is almost universal in patients receiving lithium therapy T/F

 

Alphaxalone

althesin

Here is an advertisment for Althesin® from the BJA June 1974

Are you thinking that I have lost my mind – why am I asking about a drug  whose preparation Althesin® was removed from the market in the 1980s?

Have you thought about why it was removed (probably yes)? Why didn’t the propofol solution work for alphaxalone? Does alphaxalone offer any potential benefits as an induction or TIVA agent over propofol? How is it that it is commonly still used in veterinary anaesthesia?

I don’t think that you would be examined on any of this in 2019, but the hospital I work at is currently involved in a clinical trial using alphaxalone (solubilised in a cyclodextran) TIVA and comparing it to either propofol TIVA or a volatile based anaesthetic, so in 10 years time who knows??

For those of you interested in the answers to the following statements, you could start by reading this this editorial . I couldn’t really find much in the standard texts on it….

I can’t really justify adding an LO to this but perhaps IT_GS1.1 at a stretch

Alphaxalone is a GABA-A agonist T/F

It was removed from the market in the 1980s because of the high rate of hypersensitivity reactions caused by the presence of Cremophor EL, used to aid solubility T/F

Alphaxalone causes similar reductions in SVR to propofol in doses which are equipotent for sedation T/F

Alphaxalone is a potent analgesic T/F

Alphaxalone is rapidly metabolised making it suitable for use as TIVA T/F

 

 

 

Coats of Arms and Mottoes

Now that the written exam is over, you might welcome a fun distraction in the form of Coats of Arms and mottoes. These are full of symbolism and history, and it is always fascinating to learn about the many layers of meaning that they each have.

Below are 5 examples related to anaesthesia. Can you guess them (and have a guess at the English translation of the motto)?

(1)  Corpus Curare Spiritumque

ANZCA-Crest

(2)  Fax Mentis Incendium Gloriae

RACS coat of arms

(3)  Divinum Sedare Dolorem

RCA coat of arms

(4)  Salus Dum Vigilamus

College-of-Anaesthetists Ireland coat of arms

(5)  Mente Perspicua Manuque Apta

RCPS Canada coat of arms

 

ANSWERS

(1) Hopefully you all spotted this one straight away as the Australian and New Zealand College of Anaesthetists! The motto translates as “to care for the body and its breath of life”. To read more about our College crest, click here.

(2) This one is the Royal Australasian College of Surgeons. Why, you may ask, is that included here? Many trainees don’t realise that ANZCA has only existed since 1992. Before that, we existed as the Faculty of Anaesthetists in the Royal Australasian College of Surgeons. So the FFARACS diploma had the surgeons’ crest on top! The RACS motto translates as “the torch of the mind is the flame of glory”. Hmmm…

(3) This one is the Royal College of Anaesthetists in the UK. The motto translates as “it is divine to alleviate pain”.

(4)  This is the College of Anaesthetists of Ireland. The motto translates as “safety while we watch”.

(5) This one is the Royal College of Physicians and Surgeons of Canada. All medical specialties in Canada come under the single Royal College. Fellows use either FRCPC or FRCSC depending on the specialty. Anesthesiologists use FRCPC. The motto translates as “with a keen mind and skillful hand”.

Which of the mottoes appeals to you the most? Perhaps you have an alternate favourite – maybe your school or university motto? 

Apothecaries’ System of Measurement

Australia formally adopted the metric system of measurement in 1971. Before that, the British Imperial system of measurement was in common use, with such units as ounces and pounds for mass; and yards and miles for length. Yet, even prior to 1971, some areas of medicine and science were beginning to adopt metric units, due to the obvious advantage of operating in base 10.

The imperial measurement system falls under a broader system called avoirdupois. Avoirdupois is derived from Old French, meaning “goods of weight”. The first trace of such a system seems to have originated in England circa 1300, and was used for weighing wool. Over the centuries, many variations in measurement systems evolved. These differed between countries (even regions), and industries.

One sub-set of the avoirdupois system, was the Apothecaries’ system of measurement, used in drug dispensing. (Apothecary is an historical term for a person we would now call a pharmacist.)

The Apothecaries’ units of measurement for weight included the – grain, scruple, drachm, ounce, and pound.

The smallest unit – the grain – was based on the mass of an ideal single grain of barley. It was equivalent to 64.79891 mg in the current metric system. Most drug prescriptions were written with grains as the dose unit to be given.

Consider the following pre-medication order, written on an anaesthetic record in 1944. The prescription is morphine 1/6 grain, and atropine 1/100 grain, both to be given IM three quarters of an hour preoperatively. Can you work out the milligram equivalents for the morphine and atropine, based on the conversion factor above?

apothecary

The anaesthetic would have been induced and maintained with ether. Can you think of any advantages and disadvantages of the morphine pre-med? Why do you think the atropine was necessary?

Answers about Archie and his airway

The Laryngeal Mask Airway (LMA) was just one of numerous patents that Brain applied for.  This is true. The LMA was the thirteenth patent he applied for. While not gifted in the sciences at school he had a flair for construction. He built his own guitar at the age of fourteen.

The first published study involving the LMA was a case series of women undergoing gynaecological laparoscopy.  This is also true. The paper was published in the BJA in 1983 and was titled “The laryngeal mask- a new concept in airway management”.

The LMA was first commercially available in 1983. False. The first commercial devices were available in the UK in 1988. Not all that long ago really! It took years for Brain to perfect his device and develop it as a medical device.

Australia was the first place to use the Proseal LMA.  This is true and was again relatively recently in 2000. I don’t know why. Perhaps he knew he had a willing advocate down under in the person of Joe Brimacombe!

There are over twenty different methods described to insert a LMA. This is true and they are all described in Brimacombe’s book. You only need one, however.

Dr Brain was born on July 2, 1942. His father was a diplomat and was knighted. Surely his son deserves a knighthood also?

5 things you probably didn’t know about Archie Brain

I hope I am not being presumptuous in assuming that all of you know who Archie Brain is. The next sentence will give you a rather substantial clue regardless. I reckon his invention of the laryngeal mask was worthy of the Nobel Prize for Medicine. His invention is certainly the most significant advance in the field of anaesthesia for my generation. It is very fortunate that propofol joined the arsenal at roughly the same time. White stuff + LMA is probably the commonest anaesthetic combo in the world today. Interestingly enough the first anaesthetics using the LMA were done with a combination of thiopentone and muscle relaxant. Trying to insert a LMA with just thiopentone is fraught with peril but the contemporary anaesthetic trainee has barely seen a vial of thiopentone these days let alone tried to insert a LMA under the influence of this venerable barbiturate. For a fascinating and comprehensive history about all things concerning Brain and his invention one should consult Joe Brimacombe’s definitive Laryngeal Mask Anesthesia: Principles and Practice. I would confidently assert that Brimacombe has inserted more LMAs than anyone else on the planet. Despite the American spelling of his textbook he is a pom who practices in Far North Queensland. To say he is an ardent fan of the Proseal LMA would be an understatement. LMAs are so popular in Cairns that they mandate intubating people each April so they don’t forget what to do with a laryngoscope.

The Laryngeal Mask Airway (LMA) was just one of numerous patents that Brain applied for.  TRUE/ FALSE

The first published study involving the LMA was a case series of women undergoing gynaecological laparoscopy.  TRUE/ FALSE

The LMA was first commercially available in 1983.  TRUE/ FALSE

Australia was the first place to use the Proseal LMA.  TRUE/ FALSE

There are over twenty different methods described to insert a LMA.  TRUE/ FALSE

James Young Simpson

 

IMG_20170526_143743

Still in holiday snap mode, but also anaesthesia history mode. Not examinable but here’s an opportunity to be sucked into the maw of wikipedia should you wish some guilt free distraction from study…

Simpson is credited with introducing chloroform as an anaesthetic agent for humans      TRUE/FALSE

Simpson made important developments in obstetric forceps      TRUE/FALSE

The first recorded use of chloroform for anaesthesia was direct injection into a dog      TRUE/FALSE

The first recorded death from chloroform was a 75 year old woman      TRUE/FALSE

Simpson removed the handle of the Broad St pump      TRUE/FALSE